208 THE GENESIS OF THE DIAMOND. 



tiire, it would crack in all directions. One might argne from this 

 that it was not the expansion of gases by heat alone which caused 

 the fractures. If these fractures were due to compressed gas, as con- 

 tended by Jannettaz, one might expect this cracking to have occurred 

 while the diamond and its contained gas were exposed to the enor- 

 mous heat to which, according to the igneous theory, diamonds must 

 have been subjected. 



I had been led to believe that only light-brown or smoky stones 

 crack on being exposed to dry air, but I have lately been informed 

 by one of the old diamond miners that he had seen white stones which 

 showed the same phenomenon. There are innumerable fragments of 

 diamonds in the Kimberley pipes, and it is a question how the orig- 

 inal crystals became fractured. 



C). Sir William Crookes says that the ash left after burning a dia- 

 mond invariably contains iron as its chief constituent, and the most 

 common colors of diamonds, when most perfectly pellucid, show 

 various shades of brown and yellow from the palest *■* offcolor " to 

 almost black. These variations, he declares, accord with the theory 

 that the diamond has separated from molten iron. 



I have made exhaustive tests in order to ascertain whether dia- 

 monds contain iron, oxidized or metallic. The experiments were 

 made with a magnetic separating machine, the field magnets of 

 which attracted any mineral containing iron or iron oxides except 

 pyrites. Although some of these diamonds had the appearance 

 of being coated with iron, and others were colored dark brown and 

 deep yellow, the}^ were in no way attracted by the magnet, even when 

 excited by a strong electric current. These experiments do not, per- 

 haps, disprove the existence of iron in the diamond, but they do 

 establish the fact that the quantity is infinitesimally small. Further 

 experiments in this direction ought to be made by those who have 

 better facilities for such work than are at our disposal here in Kim- 

 berley. The experiments of Messrs, Hannay, Moissan, Friedel, Sir 

 William Crookes, and others all show that microscopic diamonds can 

 be produced artificially; but they throw very little light upon the 

 question how the diamonds in the South African craters crystallized. 



7. From what is known of the theory of crystallization, one is 

 inclined to the old Indian idea that diamonds grow like onions, 

 though much less quickly. It is hardly conceivable that diamonds, 

 such as the Koh-i-nur, the Great Mogul, the Excelsior (a Jagers- 

 fontein South African stone of 971 carats), the two largest De Beers 

 diamonds (respectively of 503 and 428.5 carats), and the Cullinan 

 from the Premier mine (3,025f carats), were formed, as the micro- 

 scopic diamonds have been, in a moment of time during the sudden 

 coolina" of molten iron. 



